Air intake system for engine

ABSTRACT

In an intake system for an engine that includes plural throttle bodies  2  to  4  having throttle valves for changing an intake passage area, the plural throttle bodies  2  to  4  include manually driven side throttle bodies  2  to  4,  which have manually driven side throttle valves  2   b  to  4   b  that are opened and closed by a throttle operation of a rider, and an electrically driven side throttle body  5,  which has an electrically driven side throttle valve  5   b  that is opened and closed by an electric motor  11,  and the intake system includes a valve opening control means  15  that controls an opening of the electrically driven side throttle valve  5   b  such that a specific output characteristic corresponding to an operating state of an engine is obtained.

TECHNICAL FIELD

The present invention relates to an intake system preferably applied to,for example, a multiple cylinder engine for a motorcycle.

BACKGROUND ART

For example, a multiple cylinder engine mounted on a motorcycle includesan intake system of a multi-throttle type having one throttle body foreach cylinder. As the intake system of this type, a manual intakesystem, in which a throttle grip and throttle valves are coupledmechanically by a throttle cable and all the throttle valves are openedand closed mechanically by a throttle grip rotating operation of arider, is generally used.

On the other hand, recently, there has also been proposed an electricintake system in which an electric motor is coupled to throttle valvesvia a link mechanism or the like, a throttle grip rotating operation ofa rider is detected, and all the throttle valves are opened and closedby the electric motor according to this detected rotating operation.

Incidentally, in both the manual type and the electric type, theconventional intake system is constituted so as to control all thethrottle valves to open and close uniformly in response to a throttlegrip rotating operation of a rider. Therefore, for example, when therider closes the throttle grip suddenly, all the throttle valves alsoclose suddenly, whereby strong engine brake acts.

However, there is a demand that, depending upon a running state, forexample at the time of approach to a corner or at the time of risingfrom the corner, for example, it is desired to make the engine brakeslightly weak even in the case in which the throttle grip is closedsuddenly or it is desired to make rising of a torque slightly gentleeven in the case in which the throttle grip is opened suddenly. In theconventional system, such a demand is coped with by a throttle griprotating operation of a rider. However, this results in a problem inthat the rider is required of an excessively high level drivingoperation.

The present invention has been devised in view of the conventionalsituation, and it is an object of the present invention to provide afuel feed system for an engine that can obtain an output characteristiccorresponding to a running state without requiring a rider of a veryhigh level driving operation.

DISCLOSURE OF THE INVENTION

An invention of claim 1 is an intake system for an engine that includesplural throttle bodies having throttle valves for changing an intakepassage area, characterized in that the plural throttle bodies includemanually driven side throttle bodies having manually driven sidethrottle valves, which are opened and closed by a throttle operation ofa rider, and an electrically driven side throttle body having anelectrically driven side throttle valve, which is opened and closed byan electric motor, and the intake system includes valve opening controlmeans that controls an opening of the electrically driven side throttlevalve such that a specific output characteristic corresponding to anoperating state of an engine is obtained.

Here, in the present invention, controlling an opening of theelectrically driven side throttle valve such that a specific outputcharacteristic corresponding to an operating state of an engine meanscontrolling an opening of the electrically driven side throttle valvesuch that, for example, in the case in which a throttle grip is closedsuddenly, in the case in which a gear is shifted down in a state of theclosed throttle grip, or in the case in which these operations areperformed while the brake is further applied, generation of engine brakecan be controlled appropriately or such that rising of an engine torquein the case in which the throttle grip is opened suddenly can becontrolled.

In addition, the present invention is applicable to both an intakesystem of a carburetor type, in which a fuel feed amount is controlledby a depression at engine manifold caused by opening and closing of thethrottle valves, and an intake system of a fuel injection type, in whicha fuel feed amount is controlled by a fuel injection valve.

An invention of claim 2 is an intake system for an engine according toclaim 1, characterized in that the valve opening control means closesthe electrically driven side throttle valve in a manner delayed by afirst time constant as the manually driven side throttle valves close.

An invention of claim 3 is an intake system for an engine according toclaim 2, characterized in that the valve opening control means closesthe electrically driven side throttle valve in a manner delayed by afirst time constant within a range up to a predetermined regulatedopening as the manually driven side throttle valves close.

An invention of claim 4 is an intake system for an engine according toclaim 2 or 3, characterized in that the valve opening control meanschanges a delay by the first time constant at the time when the brake isactuated so as to be larger than the delay by the first time constant atthe time when the brake is not actuated or changes the regulated openingat the time when the brake is actuated so as to be larger than aregulated opening at the time when the brake is not actuated.

An invention according to claim 5 is an intake system for an engineaccording to claim 2 or 4, characterized in that the valve openingcontrol means temporarily opens the electrically driven side throttlevalve to a predetermined shift-down time opening at the time ofshift-down and subsequently closes the electrically driven side throttlevalve in a manner delayed by the first time constant.

An invention according to claim 6 is an intake system for an engineaccording to claim 1, characterized in that the valve opening controlmeans opens the electrically driven side throttle valve in a mannerdelayed by a second time constant as the manually driven side throttlevalves open.

An invention according to claim 7 is an intake system for an engineaccording to any one of claims 1 to 6, characterized in that the valveopening control means makes an opening of the electrically driven sidethrottle valve identical with an opening of the manually driven sidethrottle valves when a vehicle speed is lower than a predeterminedcontrol lower limit speed or a gear is in neutral.

An invention according to claim 8 is an intake system for an engineaccording to any one of claims 1 to 7, characterized in that the intakesystem learns fully-closed positions of the manually driven sidethrottle valves and the electrically driven side throttle valve to makethe fully-closed positions identical with each other when a vehiclespeed is lower than a predetermined learning time vehicle speed and anopening of the manually driven side throttle valves is smaller than apredetermined learning time opening.

Here, the learning of the fully-closed positions is performed by, forexample, in the case in which detected openings of the manually drivenside and the electrically driven side throttle valves are larger than afully-closed opening stored value, keeping the stored value as it is,and in the case in which the openings are smaller than the fully-closedopening stored value, updating the stored value.

An invention according to claim 9 is an intake system according to anyone of claims 1 to 8, characterized in that the intake system learns afully-closed position and a fully-opened position of the electricallydriven side throttle valve and drives the electric motor only betweenthe learned fully-closed position and fully opened position.

Here, the learning of the fully-closed position is performed by, forexample, in the case in which a detected opening of the electricallydriven side throttle valve is larger than a fully-closed opening storedvalue, keeping the stored value as it is, and in the case in which theopening is smaller than the fully-closed opening stored value, updatingthe stored value. In addition, the learning of the fully-opened positionis performed by, for example, in the case in which a detected opening ofthe electrically driven side throttle valve is smaller than afully-opened opening stored value, keeping the stored value as it is,and in the case in which the opening is larger than the fully-openedopening stored value, updating the stored value.

An invention of claim 10 is an intake system for an engine according toany one of claims 1 to 9, characterized in that the intake systemfurther includes a mechanical return mechanism that forcibly closes theelectrically driven side throttle valve to a predetermined returnopening as the manually driven side throttle valves close.

An invention of claim 11 is an intake system for an engine according toclaim 10, characterized in that the intake system learns a returnopening range, in which the electrically driven side throttle valve isforcibly closed by the return mechanism, and drives the electric motoronly in an opening range excluding the learned return opening range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a carburetor unit of a fuel feed system ofthe present invention.

FIG. 2 is a front view of the carburetor unit.

FIG. 3 is a sectional side view (sectional view along line III-III inFIG. 2) of the carburetor unit.

FIG. 4 is a sectional side view (sectional view along line IV-IV in FIG.2) of the carburetor unit.

FIG. 5 is a sectional side view of a main part of the carburetor unit.

FIG. 6 is a sectional side view of the main part of the carburetor unit.

FIG. 7 is a throttle valve opening characteristic chart of the fuel feedsystem.

FIG. 8 is a throttle valve opening characteristic chart of the fuel feedsystem.

FIG. 9 is a throttle valve opening characteristic chart of the fuel feedsystem.

FIG. 10 is a throttle valve opening characteristic chart of the fuelfeed system.

FIG. 11 is a block diagram of the fuel feed system.

FIG. 12 is a flowchart for explaining operations of the fuel feedsystem.

FIG. 13 is a flowchart for explaining operations of the fuel feedsystem.

FIG. 14 is a flowchart for explaining operations of the fuel feedsystem.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be hereinafter explained onthe basis of the attached drawings.

FIGS. 1 to 14 are diagrams for explaining an intake system for amotorcycle engine according to an embodiment of the present invention.FIGS. 1 and 2 are a plan view and a front view of the intake system,FIGS. 3 and 4 are sectional side views of the intake system, FIGS. 5 and6 are enlarged view of main parts, FIGS. 7 to 10 are characteristiccharts of a throttle opening for explaining operations, FIG. 11 is ablock diagram, and FIGS. 12 to 14 are flowcharts for explainingoperations.

In FIGS. 1 to 6, reference numeral 1 denotes a carburetor unitconstituting a hardware portion of the intake system of this embodiment.This carburetor unit 1 is formed by integrally combining first to fourthcarburetors 2 to 5, which are connected to intake manifolds of first tofourth cylinders, with bolting.

The respective carburetors 2 to 5 are formed by integrally combiningfirst to fourth throttle valves 2 b to 5 b of a slide type that open andclose to control passage areas of Venturi passages (intake passages) 2 ato 5 a, throttle bodies 2 d to 5 d incorporating the first to the fourththrottle valves 2 b to 5 b, and float chambers 2 e to 5 e. Valve shafts2 c to 5 c, which slide the respective throttle valves 2 b to 5 b, forman identical straight line. The valve shafts 2 c to 4 c of the first tothe third carburetors 2 to 4 are coupled to one another so as to rotatesimultaneously, and the valve shaft 5 c of the fourth carburetor 5 isadapted to rotate independently. In addition, a biasing spring 9 a,which biases the valve shafts 2 c to 4 c of the first to the thirdcarburetors 2 to 4 to rotate to a fully-closed position, is disposedbetween the second carburetor 3 and the third carburetor 4.

The valve shafts 2 c to 4 c of the first to the third carburetors arecoupled to a drive shaft 7 via a link mechanism 6. Specifically, thislink mechanism 6 has a structure in which an arm 6 a fixed to the valveshaft 3 c and an arm 6 c fixed to the drive shaft 7 are coupled by abar-like link 6 b so as to be rotatable relatively.

A throttle pulley 8 is mounted at the left end in FIG. 2 of the driveshaft 7 via an opening adjustment mechanism 9 b so as to rotate with thedrive shaft 7. Although not shown in the figure, the throttle pulley 8is coupled to a throttle grip, which is mounted on a steering handle, bya throttle cable.

With the above-mentioned structure, when a rider rotates the throttlegrip, the throttle valves 2 b to 4 b of the first to the thirdcarburetors 2 to 4 synchronize to open and close the Venturi passages 2a to 4 a. In this way, the throttle bodies 2 d to 4 d of the first tothe third carburetors 2 to 4 serve as manually driven side throttlebodies in which throttle valves are driven to open and close by a manualrotational operation of the throttle grip by the rider. Therefore,according to circumstances, the first to the third throttle valves 2 bto 4 b are referred to as manually driven side throttle valves in thisembodiment.

In addition, the valve shaft 5 c of the fourth carburetor 5 is coupledto an output shaft 11 a of an electric motor 11 via a link mechanism 10.Specifically, this link mechanism 10 has a structure in which an arm 10a fixed to the valve shaft 5 c and an arm 10 c fixed to the output shaft11 a are coupled by a bar-like link lob so as to be rotatablerelatively.

Consequently, the throttle valve 5 b of the fourth carburetor 5 opensand closes the Venturi passage 5 a according to the rotation of theelectric motor 11. In this way, the throttle body 5 d of the fourthcarburetor 5 serves as an electrically driven side throttle body inwhich a throttle valve is driven to open and close by the electric motor11. Therefore, in this embodiment, according to circumstances, thefourth throttle valve 5 b is referred to as an electrically driven sidethrottle valve.

Further, the drive shaft 7 and the output shaft 11 a of the electricmotor 11 are coupled by a mechanical return mechanism 12 that forciblycloses the electrically driven side throttle valve 5 b within apredetermined return opening range (e.g., 50 degrees) following aclosing operation of the manually driven side throttle valves 2 b to 4b.

The return mechanism 12 has a detailed structure described below. A linkmember 12 b implanted with a pressing bolt 12 a is fixed at the rightend of the drive shaft 7, and a cylindrical transmission member 12 c ismounted further on a tip side of the drive shaft 7 than the link member12 so as to be rotatable relatively. A pressing piece 12 d isprotrudingly provided in the transmission member 12 c so as to be ableto be pressed by the pressing volt 12 a. Moreover, a pressing piece 12d′, which is protrudingly provided in the transmission member 12 c, iscoupled to the arm 10 c of the link mechanism 10 via a transmission bolt12 e and a spring 12 f.

Here, FIGS. 5 and 6 show a state in the case in which the first to thefourth throttle valves 2 b to 5 b are in a fully-opened state. In thiscase, an offset opening of about 30 degrees is formed between thepressing bolt 12 a and the pressing piece 12 d. Thus, the pressing bolt12 a does not come into abutment against the pressing piece 12 d whilethe manually driven side throttle valves 2 b to 4 b close about 30degrees from a fully opened position. Therefore, it is not until themanually driven side throttle valves 2 b to 4 b rotate about 30 degreesor more from the fully opened position that the transmission member 12 calso rotates. This rotation starts forcibly close the electricallydriven side throttle valve 5 b from the pressing piece 12 d′via the arm10 c, the link 10 b, and the arm 10 a. In addition, the electricallydriven side throttle valve 5 b is still located at position with areturn opening of about 45% at a point when the manually driven sidethrottle valves 2 b to 4 b are fully closed.

In addition, a sensor 13, which detects an opening of the throttle valve2 b, is mounted at the left end in FIG. 1 of the valve shaft 2 c of themanually driven side throttle valve 2 b of the first carburetor 2.

Moreover, an electrically driven side opening sensor 14, which detectsan opening of the electrically driven side throttle valve 5 b, isdisposed on an upper end face of the fourth carburetor 5. An arm 14 b isattached to an input shaft 14 a of this electrically driven side openingsensor 14. The arm 14 b is coupled to the arm 10 a of the link mechanism10 via a link 14 c so as to be rotatable relatively.

As shown in FIG. 11, the system of this embodiment includes an ECU 15that functions as opening control means for the electrically driven sidethrottle valve 5 b. Detection signals from the manually driven sideopening sensor 13, the electrically driven side opening sensor 14, avehicle speed sensor 16, a brake pressure sensor 17, and a shiftposition sensor 18 are inputted to this ECU 15. The ECU 15 calculates anopening instruction value of the electrically driven side throttle valve5 b according to a vehicle drive state and outputs a control signal forrealizing the opening instruction value to the electric motor 11.

In addition, the ECU 15 has a failsafe processing function forperforming failure detection for a valve drive mechanism by an electricmotor on the basis of the detection signals, a synchronizing processingfunction for learning fully-closed positions of the manually driven sidethrottle valves and the electrically driven throttle valve to make boththe fully-closed positions identical, and a movable range detectionprocessing function for learning fully opened and fully-closed positionsof the electrically driven side throttle valve 5 b and a return openingby the return mechanism 12 and performing electrically driven sidethrottle valve driving by the electric motor 11 only within the learnedopening range.

Next, operations as well as actions and advantages of the system of thisembodiment will be explained.

In the system of this embodiment, while a motorcycle is running with athrottle grip fully opened (all throttle valves fully opened) and in astate of a shift position in a sixth speed, in the case in which a riderfully closes the throttle grip suddenly and changes the shift positionfrom the sixth speed to a fifth speed, . . . , a first speed todecelerate the motorcycle, throttle valve opening control shown in FIG.7 is performed. The manually driven side throttle valves 2 b to 4 b arefully closed immediately (actually, about 0.05 seconds are necessary asdescribed later) by the throttle grip fully closing operation (see acharacteristic curve A). On the other hand, the electrically driven sidethrottle valve 5 b is forcibly closed to the vicinity of an opening 45%with a delay of very short time by the function of the return mechanism12 (see B0 of a characteristic curve B). Thereafter, the electricallydriven side throttle valve 5 b is closed in a manner delayed by a firsttime constant by the function of the ECU 15 (see B1 of thecharacteristic curve B), temporarily opened to a shift-down time opening(e.g., about 45%, B2′ of the characteristic curve B) when the motorcycleis decelerated from the sixth speed to the fifth speed, closed again ina manner delayed by the first time constant, and finally regulated to aregulated opening equivalent to about 20% of the full open (see B3 ofthe characteristic curve B).

Note that it is needless to mention that various modifications can beadopted for the characteristic curve B1 by selecting the first timeconstant appropriately. In addition, various modifications can also beadopted for the shift-down time opening and the regulated opening.

FIG. 8 shows an instance when the throttle grip is closed in enlargement(with a time axis extended). That is, the manually driven side throttlevalves 2 b to 4 b start closing as the throttle grip is closed,according to elapse of time corresponding to the offset opening(transmission free range) in the return mechanism 12 (see B0′ in FIG.8), the electrically driven side throttle valve 5 b also starts closing.When the manually driven side throttle valves are fully closed, theelectrically driven side throttle valve has an opening of about 45%.Here, the forcible closing operation ends, and after that, theelectrically driven side throttle vale closes in a manner delayed by thefirst time constant (slowly) according to the control of the ECU 15.

The ECU 15 is adapted to change the first time constant and theregulated opening according to a driving condition. FIG. 9 shows a statein which the first time constant and the regulated opening are changedfrom the time when the brake is actuated to the time when the brake isnot actuated.

A delay by the first time constant (B1) at the time when the brake isactuated (when a brake pressure signal of a front wheel braking deviceis equal to or higher than a predetermined threshold value) is changedso as to be larger than a delay by a time constant (B1′) at the timewhen the brake is not actuated (a brake pressure signal is lower thanthe threshold value), that is, such that the electrically driven sidethrottle valve closes more slowly at the time of braking than at thetime of non-braking. In addition, the regulated opening (B3) at the timewhen the brake is actuated is changed so as to be larger than aregulated opening (B3′) at the time of non-actuation.

Moreover, as indicated by a characteristic curve A′ in FIG. 10, the ECU15 is adapted to open the electrically driven side throttle valve 5 b ina manner delayed by a second time constant as the manually driven sidethrottle valves 2 b to 4 b open, that is, at the time of acceleration(see a characteristic curve C in FIG. 10). Note that it is needless tomention that various modifications can be adopted as the characteristiccurve C by selecting the second time constant appropriately.

A control operation for a fuel feed system by the ECU 15 will beexplained on the basis of flowcharts in FIGS. 12 to 14. Note that, inFIGS. 12 to 14, DBW means the electrically driven side throttle valve,and throttle means the manually driven side throttle valves.

First, an operation for alignment of fully-closed positions for themanually driven side and the electrically driven side throttle valveswill be explained on the basis of FIG. 12. When a program begins, in thecase in which an opening at the time of full close of the electricallydriven side throttle valve (DBW) has not been learned (step S1), it isjudged whether a vehicle speed does not exceed a set value (learningtime lower limit speed) and an opening of the manually driven throttlevalves exceeds a set value (learning time lower limit opening) (stepS2). If both the vehicle speed and the manually driven side throttlevalve opening do not exceed the set values, that is, if the speed issufficiently low and the throttle opening is sufficiently small, the ECU15 outputs a duty in a direction for closing the electrically drivenside throttle valve (step S3). If the detected opening of theelectrically driven side throttle valve is larger than a fully-closedopening stored value of the valve, the ECU 15 keeps the stored value asit is, and if the opening of the electrically driven side throttle valveis smaller than the fully-closed opening stored value, the ECU 15updates the fully-closed opening stored value to the detected value(steps S4 and S5). When a predetermined set time elapses, the ECU 15ends fully-closed opening learning for the electrically driven sidethrottle valve (steps S6 and S7). Then, the ECU 15 performs alignment offully-closed positions on the basis of the manually driven side throttlevalve fully-closed opening and the learned fully-closed opening of theelectrically driven side throttle valve (step S8).

If the fully-closed opening of the electrically driven side throttlevalve has been learned in step S1, the ECU 15 performs failure detectionfor the electrically driven side opening sensor and the electric motor(step S9). If failures have occurred, the ECU 15 outputs a duty in adirection for closing the electrically driven side throttle valve, andstores and displays information on these failures (steps S10 to S12).

In addition, if at least one of the vehicle speed and the throttleopening is larger than the set values in step S2, and if no failure hasoccurred in step S10, the ECU 15 performs instruction value calculationprocessing for an electrically driven side throttle valve and movablerange detection processing for the electrically driven side throttlevalve to be described later and outputs a duty corresponding to adifference between the instruction value and the detection value of theelectrically driven side throttle valve (steps S13 to S15).

Next, the opening instruction value calculation processing for theelectrically driven side throttle valve 5 b will be explained on thebasis of FIG. 13. When a program for the processing begins, if a shiftposition of a transmission is not neutral (step S21), a vehicle speed isnot equal to or lower than the set value (control lower limit speed)(step S22), a shift-down operation is not being performed (step S23), abrake is not being actuated (step S24), an electrically driven sidethrottle valve opening is not smaller than the regulated opening (B3)(step S25), a throttle valve is not being opened (step S26), and thebrake is not being applied again (step S27), that is, a motorcycle isrunning at a normal constant speed, the ECU 15 sets a value obtained byapplying a predetermined filter to the detected opening of the manualside throttle valves, that is, the opening, which is obtained bydelaying the opening of the manual side throttle valves by the firsttime constant (B1), as the opening instruction value of the electricallydriven side throttle valve (step S28).

If the shift position is neutral in step S21, and if the vehicle speedis lower than the control lower limit speed in step S22, the ECU 15 setsthe same opening as the manually driven side throttle valve opening asthe electrically driven side throttle valve opening instruction value(step S29). If the shift-down operation is performed in step S23, theECU 15 sets the shift-down time opening set value (B2′ in FIG. 7) as theopening instruction value of the electrically driven side throttle valve(step S30).

In addition, if the brake is being applied in step S24, and when thedetected manually driven side throttle valve opening is smaller than thebrake time regulated opening (see B3 in FIG. 9), the ECU 15 sets theregulated opening as the opening instruction value of the electricallydriven side throttle valve (steps S31 and S32). When the detectedmanually driven side throttle valve opening is not smaller than thebrake time regulated opening, the ECU 15 returns to step S26.

Further, if the manually driven side throttle valve opening is smallerthan the regulated value (see B3 in FIG. 7) in step S25, the ECU 15 setsthis regulated value as the opening instruction value of theelectrically driven side throttle valve (step S33).

Moreover, if the manually driven side throttle valve is being opened instep S26, the ECU 15 sets an opening, which is obtained by delaying thedetected manually driven side throttle valve opening by the second timeconstant (an opening obtained by filtering the manually driven sidethrottle valve opening, see the curve C in FIG. 10), as the openinginstruction value of the electrically driven side throttle valve (stepS34). If the brake is being applied in step S27, the ECU 15 sets anopening, which is obtained by delaying by the brake actuation timeconstant (B1 in FIG. 9) (an opening obtained by filtering), as theinstruction value (step S35).

Then, the ECU 15 compares the instruction value calculated by each ofthe steps with a sum of the manually driven side throttle vale openingand the offset opening. If the instruction value is not larger than thissum, the ECU 15 sets the calculated value as the instruction valuedirectly, and if the instruction value is larger than the sum, the ECU15 replaces the instruction value with this sum (steps S36 and S37).

In addition, the ECU 15 compares the calculated instruction value withthe fully-opened opening learned value of the electrically driven sidethrottle valve. If the instruction value is not larger than this learnedvalue, the ECU 15 sets the calculated value as the instruction valuedirectly, and if the instruction value is larger than this learnedvalue, the ECU 15 replaces the instruction value with the learned value(steps S38 and S39).

Moreover, the ECU 15 compares the calculated instruction value with thefully-closed side learned value of the electrically driven side throttlevalve. If the instruction value is not smaller than this learned value,the ECU 15 sets the calculated value as the instruction value directly,and if the instruction value is smaller than this learned value, the ECU15 replaces the instruction value with the learned value (steps S40 andS41).

Detection processing for a movable range of the electrically driven sidethrottle valve will explained on the basis of FIG. 14. First, a detectedelectrically driven side throttle valve opening is compared with afully-closed opening stored value of the electrically driven sidethrottle valve. If the detected value is larger than the stored value,the stored value is not changed, and if the detected value is not larger(is smaller) than the stored value, the stored value is replaced withthe detected value (steps S51 and S52).

Next, the detected electrically driven side throttle valve opening iscompared with a fully-opened opening stored value of the electricallydriven side throttle valve. If the detected value is smaller than thestored value, the stored value is not changed, and if the detected valueis not smaller (is larger) than the stored value, the stored value isreplaced with the detected value (steps S53 and S54).

Subsequently, a difference between the detected manually driven sidethrottle valve opening and the electrically driven side throttle valveopening is compared with an offset opening stored value of theelectrically driven side throttle valve. If the difference is smallerthan the stored value, the stored value is not changed, and if thedifference is not smaller (is larger) than the stored value, the offsetopening stored value is replaced with this difference (steps S53 andS54).

As described above, in this embodiment, an opening of the electricallydriven side throttle valve 5 b is controlled such that a specific outputcharacteristic corresponding to an operating state of an engine isobtained. Thus, an output characteristic of an engine corresponding to adriving condition can be obtained without requiring a rider of anexcessively high level driving operation, and a driving operation can befacilitated.

More specifically, the electrically driven side throttle valve 5 b isclosed in a manner delayed by the first time constant (see B1 in FIG. 7)as the manually driven side throttle valves 2 b to 4 b close accordingto a throttle grip operation of the rider, and not to close theregulated opening (B3 in FIG. 7). Thus, even in the case in which therider closes the throttle grip suddenly, the electrically driven sidethrottle valve 5 b closes later than the throttle grip operation, andgeneration of engine brake can be controlled so much more for that.Therefore, the rider is not required an excessively high level drivingoperation, and a driving operation is facilitated.

In addition, the first time constant at the time when the brake isactuated (B1 in FIG. 9) is changed to a time constant that makes thedelay larger than that of the time constant at the time when the brakeis not actuated (B1′ in FIG. 9), and the regulated opening at the timewhen the brake is actuated (B3) is changed so as to be larger than theregulated opening at the time when the brake is not actuated (B3′).Thus, in the case in which the rider actuates the brake device,generation of engine brake is controlled stronger than in the case inwhich the rider does not actuate the brake device, and a drivingoperation can be facilitated.

It is said that, in general, or depending upon preference of in drivingoperation of the rider, driving is easier when engine brake is notgenerated much in the case in which a brake is applied strongly. In thisembodiment, the system can cope with such a situation as well.

The electrically driven side throttle valve 5 b is temporarily opened toa predetermined shift-down time opening (B2′ in FIG. 7) and subsequentlyclosed in a manner delayed by the first time constant (B1). Thus, shockdue to a sudden increase in engine brake at the time of shift-down canbe eased, and driving can be facilitated.

In addition, the electrically driven side throttle valve 5 b is openedin a manner delayed by a second time constant (see a characteristiccurve C in FIG. 10) as the manually driven side throttle valves 2 b to 4b open. Thus, even in the case in which a rider opens the throttle gripsuddenly, excessively steep rising of an engine torque can becontrolled, and a driving operation can be facilitated.

Further, an opening of the electrically driven side throttle valve 5 bis made identical with an opening of the manually driven side throttlevalves 2 b to 4 b when a vehicle speed is lower than a predeterminedcontrol lower limit speed or when a gear is in neutral. Thus, it ispossible to avoid unnecessary control in a driving range in whichspecial control for a throttle valve opening is not originally requiredas at the time of low-speed running or neutral.

Moreover, the intake system learns fully-closed positions of themanually driven side throttle valves 2 b to 4 b and the electricallydriven side throttle valve 5 b, and the fully-closed positions are madeidentical with each other according to-this learned value. Thus, even ifthere is an error between the manually driven side throttle openingsensor 13 and the electrically driven side throttle opening sensor 14,both the throttle valves can be synchronized, and control accuracy canbe improved.

The intake system learns a fully-closed position and a fully-openedposition of the electrically driven side throttle valve 5 b and drivesthe electric motor 11 only between the learned fully-closed position andfully opened position. Thus, the problem in that the electrically drivenside throttle valve 5 b is driven exceeding the fully-closed positionand the fully-opened position can be avoided, and breakage due tofurther energization in a lock state of the electric motor 11 can beavoided.

The intake system further includes the mechanical return mechanism 12that forcibly closes the electrically driven side throttle valve 5 b toa predetermined return opening as the manually driven side throttlevalves 2 b to 4 b close. Thus, control by the electric motor 11 is alsounnecessary for the electrically driven side throttle valve 5 b up tothe return opening, and control for an opening of the electricallydriven throttle valve can be simplified.

Moreover, the intake system learns a return opening range, in which theelectrically driven side throttle valve 5 b is forcibly closed by thereturn mechanism 12, and drives the electric motor 11 only in an openingrange excluding this return opening range. Thus, lock breakage of theelectrically driven side throttle valve 5 b caused by driving theelectric motor 11 in the forcible return range can be avoided.

Note that, although the intake system of the carburetor type isexplained in the embodiment, the present invention can also be appliedto an intake system of a fuel injection type. In addition, although thecase in which throttle bodies are formed separately and combined by abolt is described, it is also possible to form all or a part of thethrottle bodies integrally.

Industrial Applicability

According to the invention of claim 1, the plural throttle bodiesinclude manually driven side throttle bodies and electrically drivenside throttle body, and the intake system controls an opening of theelectrically driven side throttle valve such that a specific outputcharacteristic corresponding to an operating state of an engine isobtained. Thus, generation of engine brake, for example, in the case inwhich a throttle grip is closed suddenly or in the case in which a gearis shifted down can be controlled, or rising of an engine torque in thecase in which the throttle grip is opened suddenly can be controlled. Anoutput characteristic corresponding to a driving condition can beobtained without requiring a rider of an excessively high level drivingoperation, and a driving operation can be facilitated.

According to the second invention of claim 2, the electrically drivenside throttle valve is closed in a manner delayed by a first timeconstant as the manually driven side throttle valves close. Thus, evenin the case in which a rider closes the throttle grip suddenly, theelectrically driven side throttle valve closes later than a throttlegrip operation, and generation of engine brake can be controlled so muchmore for that.

According to the invention of claim 3, in the case in which theelectrically driven side throttle valve is closed in a manner delayed bya first time constant as the manually driven side throttle valves close,the electrically driven side throttle valve is closed in a range up to apredetermined regulated opening. Thus, generation of engine brake can becontrolled more surely.

According to the invention of claim 4, a delay by the first timeconstant at the time when the brake is actuated is changed so as to belarger than the delay by the first time constant at the time when thebrake is not actuated or the regulated opening at the time when thebrake is actuated is changed so as to be larger than a regulated openingat the time when the brake is not actuated. Thus, in the case in which arider actuates a brake device, generation of engine brake is controlledmore strongly than in the case in which the rider does not actuate thebrake device, and a driving operation can be further facilitated. It issaid that, in general, or depending upon preference of in drivingoperation of the rider, driving is easier when engine brake is notgenerated much in the case in which a brake is applied strongly. Thepresent invention can facilitate driving in such a case.

According to the invention of claim 5, at the time of shift-down, theelectrically driven side throttle valve is temporarily opened to apredetermined shift-down time opening and subsequently closed in amanner delayed by the first time constant. A sudden increase in enginebrake at the time of shift-down can be controlled, and shock at the timeof shift-down can be eased to facilitate deriving.

According to the invention of claim 6, the electrically driven sidethrottle valve is opened in a manner delayed by a second time constantas the manually driven side throttle valves open. Thus, even in the casein which a rider opens the throttle grip suddenly, excessively steeprising of an engine torque can be controlled, and a driving operationcan be facilitated.

According to the invention of claim 7, an opening of the electricallydriven side throttle valve is made identical with an opening of themanually driven side throttle valves when a vehicle speed is lower thana predetermined control lower limit speed or when a gear is in neutral.Thus, it is possible to avoid unnecessary control in a driving range inwhich special control for a throttle valve opening is not originallyrequired as at the time of low-speed running or neutral.

According to the invention of claim 8, the intake system learnsfully-closed positions of the manually driven side throttle valves andthe electrically driven side throttle valve when a vehicle speed islower than a predetermined learning time speed and an opening of themanually driven side throttle valves is smaller than a predeterminedlearning time opening. Thus, the learning of the fully-closed positionscan be performed surely. In addition, the fully-closed positions aremade identical with each other according to the learned value, wherebyeven if there is an error between a manually driven side throttleopening sensor and an electrically driven side throttle opening sensor,both the throttle valves can be synchronized, and control accuracy canbe improved.

According to the invention of claim 9, the intake system learns afully-closed position and a fully-opened position of the electricallydriven side throttle valve and drives the electric motor only betweenthe learned fully-closed position and fully opened position. Thus, lockbreakage of the electric motor, which is caused by driving theelectrically driven side throttle valve exceeding the fully-closedposition and the fully-opened position, can be avoided.

According to the invention of claim 10, the intake system furtherincludes a mechanical return mechanism that forcibly closes theelectrically driven side throttle valve to a predetermined returnopening as the manually driven side throttle valves close. Thus, controlby the electric motor is also unnecessary for the electrically drivenside throttle valve up to the return opening, and control for an openingof the electrically driven throttle valves can be simplified.

According to the invention of claim 11, the intake system drives theelectric motor only in an opening range excluding a return opening rangein which the electrically driven side throttle valve is forcibly closedby the return mechanism. Thus, lock breakage of the electric motor canbe avoided.

1. An intake system for an engine, comprising: plural throttle bodiesconstituted by manually driven side throttle bodies having manuallydriven side throttle valves, which are opened and closed by a throttleoperation of a rider; an electrically driven side throttle body havingan electrically driven side throttle valve, which is opened and closedby an electric motor; and a valve opening control means for closing anopening of the electrically driven side throttle valve in a mannerdelayed by a first time constant within a range up to a predeterminedregulated opening as the manually driven side throttle valves close.2-11. (canceled)
 12. The intake system for an engine according to claim1, wherein the valve opening control means changes a delay by the firsttime constant at a time when a brake is actuated so as to be larger thanthe delay by the first time constant at a time when the brake is notactuated or changes a regulated opening at the time when the brake isactuated so as to be larger than a regulated opening at the time whenthe brake is not actuated.
 13. The intake system for an engine accordingto claim 1, wherein the valve opening control means temporarily opensthe electrically driven side throttle valve to a predeterminedshift-down time opening at a time of shifting-down and subsequentlycloses the electrically driven side throttle valve in a manner delayedby the first time constant.
 14. An intake system for an engine,comprising: plural throttle bodies constituted by manually driven sidethrottle bodies having manually driven side throttle valves, which areopened and closed by a throttle operation of a rider; an electricallydriven side throttle body having an electrically driven side throttlevalve, which is opened and closed by an electric motor; and a valveopening control means, which controls an opening of the electricallydriven side throttle valve such that a specific output characteristiccorresponding to an operating state of an engine is obtained, and learnsfully-closed positions of the manually driven side throttle valves andthe electrically driven side throttle valve to make the fully-closedpositions identical with each other when a speed is lower than apredetermined learning time speed and an opening of the manually drivenside throttle valves is smaller than a predetermined learning timeopening.
 15. The intake system for an engine according to claim 14,wherein the intake system learns a fully-closed position and afully-opened position of the electrically driven side throttle valve anddrives the electric motor only between the learned fully-closed positionand fully-opened position.
 16. An intake system for an engine,comprising: plural throttle bodies constituted by manually driven sidethrottle bodies having manually driven side throttle valves, which areopened and closed by a throttle operation of a rider; an electricallydriven side throttle body having an electrically driven side throttlevalve, which is opened and closed by an electric motor; and a valveopening control means, which controls an opening of the electricallydriven side throttle valve such that a specific output characteristiccorresponding to an operating state of an engine is obtained, andincludes a mechanical return mechanism that forcibly closes theelectrically driven side throttle valve to a predetermined returnopening as the manually driven side throttle valves close.
 17. Theintake system for an engine according to claim 16, wherein the intakesystem learns a return opening range, in which the electrically drivenside throttle valve is forcibly closed by the return mechanism, anddrives the electric motor only in an opening range excluding the learnedreturn opening range.
 18. An intake system for an engine, comprising:plural throttle bodies constituted by manually driven side throttlebodies having manually driven side throttle valves, which are opened andclosed by a throttle operation of a rider; an electrically driven sidethrottle body having an electrically driven side throttle valve, whichis opened and closed by an electric motor; and a valve opening controlmeans that closes the electrically driven side throttle valve in adelayed manner as the manually driven side throttle valves close andchanges a delay at a time when the brake is actuated so as to be largerthan the delay at a time when the brake is not actuated.
 19. An intakesystem for an engine, comprising: plural throttle bodies constituted bymanually driven side throttle bodies having manually driven sidethrottle valves, which are opened and closed by a throttle operation ofa rider; an electrically driven side throttle body having anelectrically driven side throttle valve, which is opened and closed byan electric motor; and a valve opening control means that closes theelectrically driven side throttle valve in a delayed manner as themanually driven side throttle valves close and temporarily opens theelectrically driven side throttle valve to a predetermined shift-downtime opening at a time of shifting-down and subsequently closes theelectrically driven side throttle valve later than the manually drivenside throttle valves.
 20. An intake system for an engine, comprising:plural throttle bodies constituted by manually driven side throttlebodies having manually driven side throttle valves, which are opened andclosed by a throttle operation of a rider; an electrically driven sidethrottle body having an electrically driven side throttle valve, whichis opened and closed by an electric motor; and a valve opening controlmeans that closes the electrically driven side throttle valve in amanner delayed within a range up to a predetermined regulated opening asthe manually driven side throttle valves close.
 21. The intake systemfor an engine according to claim 20, wherein the valve opening controlmeans closes the electrically driven side throttle valve in a mannerdelayed by a first time constant as the manually driven side throttlevalves close.
 22. The intake system for an engine according to claim 20,wherein the valve opening control means opens the electrically drivenside throttle valve in a manner delayed by a second time constant as themanually driven side throttle valves open.
 23. The intake system for anengine according to claim 20, wherein the valve opening control meansmakes an opening of the electrically driven side throttle valveidentical with an opening of the manually driven side throttle valveswhen a speed is lower than a predetermined control lower limit speed ora gear is in neutral.
 24. The intake system for an engine according toclaim 21, wherein the valve opening control means makes an opening ofthe electrically driven side throttle valve identical with an opening ofthe manually driven side throttle valves when a speed is lower than apredetermined control lower limit speed or a gear is in neutral.
 25. Theintake system for an engine according to claim 22, wherein the valveopening control means makes an opening of the electrically driven sidethrottle valve identical with an opening of the manually driven sidethrottle valves when a speed is lower than a predetermined control lowerlimit speed or a gear is in neutral.
 26. The intake system for an engineaccording to claim 1, wherein the engine includes plural throttle bodieshaving throttle valves for changing an intake passage area.
 27. Theintake system for an engine according to claim 14, wherein the engineincludes plural throttle bodies having throttle valves for changing anintake passage area.
 28. The intake system for an engine according toclaim 16, wherein the engine includes plural throttle bodies havingthrottle valves for changing an intake passage area.
 29. The intakesystem for an engine according to claim 18, wherein the engine includesplural throttle bodies having throttle valves for changing an intakepassage area.
 30. The intake system for an engine according to claim 19,wherein the engine includes plural throttle bodies having throttlevalves for changing an intake passage area.